try_compile: Add signature to allow multiple SOURCES

Extend the signature

 try_compile(RESULT_VAR <bindir> <srcfile> ...)

to allow multiple sources as

 try_compile(RESULT_VAR <bindir> SOURCES <srcfile>... ...)

Process the sources to generate a CMakeLists.txt that enables all needed
languages.

Teach the TryCompile test to try cases with two sources of the same
language and of mixed languages.  Teach RunCMake.try_compile to cover
error cases for the signature.
Merge topic 'add-try_compile-options' into next

482f112 try_compile: Add signature to allow multiple SOURCES